hmf/rejetting questions

[homemadebrownie]

i have just bought an hmf sport series complete with a dyno jet kit...in the faq its not for dyno jets so i was wondering does anybody no the jetting specs for the 250ex with dyno jetting...i mostly need to know the main jet....thanks

[tedwilley]

You need to consider your elevation above sea level to start. Also, whether or not your air box lid is on or off, and if you have a K&N/UNI type filter. All these factors affect your air flow and air to fuel ratio.
I have an HMF full system, no airbox lid, K&N with an Outerwear filter cover, and I ride between 200 and 3000 feet above sea level. I also am running an AMR revbox, but the jetting did not change with the revbox:
I have the stock pilot jet, Dynojet needle on the third clip, Dynojet 112 main, fuel screw 2 -3/4 turns out. Runs great, no popping or bogging.

The best way for a home mechanic to jet accurately is first buy a new spark plug. Before you install it, install the jets you believe will be about right. Then install the plug and run between 1/2 and full throttle (up and down not steady) for about ten minutes. Remove the plug and see what color the porcelain is. Light tan is perfect. White is lean, black and/or wet is too rich. Too lean go up size, too rich go down a size, and retest. Also, notice if you are popping on deceleration. This is almost always too lean. If you are popping, bogging, or missing; at 1/2 to 3/4 throttle it is the needle clip. At WOT it is the main.
There are threads on the forum about 'reading spark plugs'

[homemadebrownie]

on the hmf website it said to put it as 125 main...and btw do u have a 250ex

[tedwilley]

Yes, an 07 250ex.
IMO, a 125 is ridiculously large, without other mods. Remember the higher above sea level, the less air, so the mixture gets richer quickly.

http://i195.photobucket.com/albums/z86/NotSoYoungAnymore/HPIM0204.jpg

[homemadebrownie]

i have a k&n airfilter


i live under 5000ft above sealevel so needle 4th place
below 3000ft for the main jet screw
and i live under 5000ft so the 2.5 turns out for the air/fuel mixture screw

with all this info plz tell me if 125 main is good and give me any other suggestions

btw give me some info on the pilot jet and what i should do to that

[klutchbuster250]

i got a hmf also and i was origanaly with a 150 but that was ridiculosly high and now if im not mistaken im at a 125 and its good i also run no lid or slotted airbox lid with a uni filter and i get just a lil poping when i engine brake and let go the throtle but nothing seriouse

[homemadebrownie]

did it backfire at all at 150

and when i rejet which one should i try first

[tedwilley]

Rule of thumb for the pilot jet:
If you can adjust it with the mixture screw, use the current pilot jet.
If you are all the way in, go a size smaller.
If you are all the out out, go a size bigger.

BTW, you can see all of the different sizes that are working for others with basically the same engine, so you will have to use trial and error to get it right for you.
Adjusting the needle is a five minute procedure, changing the main, about ten minutes.

[homemadebrownie]

how do u change the needle and whats the e washer thingy

[tedwilley]

Okay, one more time...
Remove the seat, remove the airbox.
Using a small pair of channel locks, unscrew the collar where the throttle cable goes into the top of the carb.
Pull up on the throttle cable to remove the throttle slide.
Hold the throttle cable assembly in one hand and grasp the throttle slide in the other hand. Push these together to compress the throttle cable spring.
The end of the cable has a cable stop (non-removable) which slides out of the slot in which it is located on the throttle slide.
This will separate the throttle slide from the throttle cable assembly, so can now disassemble the throttle slide.
Looking down into the throttle slide, you will see a plastic disk with a notch on either side. This disk is the needle retaining clip. It is inside a groove cut into the throttle slide.
See next post for detail...

[tedwilley]

Here is how to remove the needle. Be careful the parts are small, do not lose any!
Assmebly is the reverse of these instructions.
DO NOT over tighten the throttle cable collar when finished, it is 'pot' metal and can be stripped-not a good thing.:scary:

http://i195.photobucket.com/albums/z86/NotSoYoungAnymore/NeedleAssembly.jpg

[TRXRIDER4567]

Not to take over or any thing. but i have a fmf slip on and that is it airbox lid is on. do i need to rejet . also there is no popping. well only when you reb it high then let off quick.

[homemadebrownie]

nope u dont need to rejet but if u rejet ull get more power then u have now...on slip ons u dont need to rejet alot of times

[homemadebrownie]

how do i get to that part of the needle there is the spring and the throttle cable in the way

[tedwilley]

When you are holding the throttle cable with one hand, use the other hand to compress the spring by pushing your hands together. Then holding it together with one hand, use a small screwdriver or knife, or something like that to slide the end of the throttle cable down the slot in the throttle slide and out. This will allow the throttle slide top separate from the cable assembly. It is much easier to put it back together. This is the only difficult part of disassembly. After a couple of tries you will get the knack of how it works best for you.

[homemadebrownie]

ok i got the throttle cable and spring off and now im lookin at the back end of the needle but that white retainer isnt coming off

[homemadebrownie]

nvm i got it off now im working with the main jet and the air/fuel screw...how do u take the main jet screw off that long golden rod?

[homemadebrownie]

forget that to i got it...now last thing i need to know where u see the numbers one the main jet

[tedwilley]

They are stamped on the side with the screwdriver slot in it.
The numbers are VERY tiny. I don't get the different jets mixed together because it would take so long to sort them out again.
The stock is either a 94 or 96.
I run a K&N with an outerwear and no lid, I started with a 108 main jet (now a 112). If your are stock with the lid on try a 102 to start.
You probably will need to change main jets several times until you get it running to your satisfaction.

[homemadebrownie]

are the numbers stamped by the holes? and can u get me a pic if possible thanks

[tedwilley]

They are stamped around the top edge like the caliber on a bullet.
The top is the side with the screwdriver slot in it.
The new ones are in clearly marked bags.

[homemadebrownie]

im still alittle confused and also did u change ur pilot at all

[tedwilley]

No change to the pilot jet, I just adjusted my mixture screw 2-1/2 turns out (starting from all the way in).

[homemadebrownie]

so u didnt change ur main jet either?....and if u did can u turn me how many turns u did

[tedwilley]

I gave you the main jet size (112) about ten posts back.
The mixture screw adjusts the fuel from the pilot jet.
Like I already said mine is 2-1/2 turns out.

HMF Full system
K&N Filter with Outerwear
NO Airbox lid
Dynojet main jet 112
Stock pilot
Fuel screw 2-1/2 turns out
Dynojet needle on third slot
AMR revbox/CDI
150-2000 feet above sea level

[homemadebrownie]

arent u suppose to keep it 4th groove for the needle cuz ur under 5000ft

[tedwilley]

Jetting varies for each engine, even identical engines. You adjust it for the best response for each engine. One size does not fit all. The suggestions in the forum including what I've shared, are just suggestions to get you started. YOU must decide on what is right for your engine.

[homemadebrownie]

i understand but i still cant find the numbers for the main jet...and my thing just stalls when it idles with the choke off and i didnt touch my idle

[tedwilley]

Did you change your main jet?
What sizes are left in the kit that you didn't use? You can see which one is missing from the parts list that came with the kit.
Did you put the carb bowl back together right? If you made a mistake, the float could be stuck and is flooding the carb.
Retrace your steps from the beginning and see if you can find anything.
Good luck and be patient.

[homemadebrownie]

my quad runs pretty good with the choke on then when i turn it off its it stalls i think its the main jet...do u need a magnifying glass to see the main jet numbers?

[tedwilley]

I know that I need a magnifying glass. But my 13 year can read them for me.
If all you changed was the needle and the main, those would not cause you to stall at idle.
The idle speed is controlled by:
1 Pilot jet
2. Fuel screw
3. Idle screw (right side of the carb when you are sitting on the bike)
The idle screw actually moves the throttle slide up or down when you screw it in or out. That is how the idle speed is set. Disassemble the throttle slide again and make sure you put it together right. The slot where the the throttle cable end goes in should be on the left side(sitting on the bike) and the larger, shorter slot (for the idle screw) should be on the right side.

[homemadebrownie]

thanks man i got it rejetted and im running a 106 main and its working for me...but on e thing is it normal for the header to turn a goldish color?

[klutchbuster250]

yup its normal these bikes run really hot , iv had mine for almost a year and its still looking good just that golden color but its normal nothing u can do about it but make sure u let ur bike cool down befor u hose it down if not ur pipe will rust and crap

[tedwilley]

Every stainless exhaust pipe(cars motorcycles, quads) I ever seen colors with heat. The hotter the more change in color. Yours sounds about the right color.